A metal-oxide-semiconductor (MOS) transistor is one of the most important devices in modern integrated circuits. An elementary structure of the MOS transistor includes: a semiconductor substrate, gate structures on a surface of the semiconductor substrate, source doped regions in the semiconductor substrate on one side of the gate structures and drain doped regions in the semiconductor substrate on another side of the gate structures. In the MOS transistor, voltages are applied on the gate structures to control currents flowing through channels under the gate structures and to produce on/off signals.
With continuous development in semiconductor technologies, conventional planar MOS transistors have a poor controlling ability on the channel current, which causes serious leakage current. A fin field effect transistor (FinFET) is an emerging multi-gate device. A FinFET usually includes fins protruding from the surface of the semiconductor substrate, gate structures covering a portion of top surfaces and sidewalls of the fins, source doped regions in the fins on one side of the gate structures, and drain doped regions in the fins on another side of the gate structures.
However, semiconductors devices formed by either planar MOS transistors or FinFETs have poor performance. The disclosed devices and methods are directed to at least partially alleviate one or more problems set forth above and to solve other problems in the art.